(1) Field of the invention
The present invention relates to thermoplastic resin compositions and their use, and more particularly to thermoplastic resin compositions and molded articles therefrom such as car bumpers having excellent impact resistance, coating and adhering properties.
(2) Description of the Prior Art
Propylene polymers are reasonable in price and have excellent mechanical properties, moldability, chemical resistance and the like. They are widely used in many plastic molding fields. However, in the propylene polymers impact resistance, coating and adhering properties of molded articles therefrom are relatively poor, and for this reason, the range of use of such propylene polymers had certain limitations. Japanese Patent Unexamined Publication Nos. 63-39951 and 63-122752 describe a thermoplastic composition for use in car bumpers wherein a thermoplastic elastomer is blended with a propylene polymer to improve impact resistance and coating properties of molded bumpers therefrom. In coating molded propylene polymer articles, there has been widely used a method comprising cleaning the surface of said articles by the use of a halogen-contained organic solvent such as 1,1,1-trichloroethane, trichloroethylene and the like, followed by primer coating and final coating.
A method wherein a vinyl polymer is blended with a propylene polymer to improve the above-mentioned poor properties of propylene polymer has been also known. Japanese Patent Unexamined Publication No. 58-93730 discloses a improved method for dispersing a polystyrene into a propylene polymer wherein the propylene polymer is blended with a polystyrene-modified propylene polymer prepared by the use of a specific process.
As to the above-mentioned method including a cleaning step, the need exists for a new process which do not employ the halogen-containing solvent as a cleaning agent in the aspects on environmental pollution.
However, it has been known that when a noncleaning process is employed, the adhering properties of molded articles to a primer become extremely poor.
In the reference Japanese Patent Unexamined Publication No. 58-93730, only a small amount of the polystyrene can be blended with the propylene polymer because of their poor compatibilities, and the test results for molded articles from the blended composition show a tendency to become poor in impact resistance. As to the polystyrene-modified propylene polymer, it has been found that the compatibility of said resin with a propylene polymer is still insufficient because the grafting efficiency of said modified resin is relatively low.